PSI - Issue 24

Giovanna Fargione et al. / Procedia Structural Integrity 24 (2019) 758–763 G. Fargione and F. Giudice / Structural Integrity Procedia 00 (2019) 000 – 000

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field of metal components fabrication. Compared to conventional ones (such as casting, forging, and machining), AM technologies have the primary advantages of very limited geometric constraints, that allows the building of complex part designs, and low average cost for small batch size manufacturing. Furthermore, they are also considered as cleaner production techniques, due to some aspects: the parts are built layer by layer, so that raw materials use is very efficient, and material waste is minimized; the freedom in shaping allows to obtain lightweight components, saving raw materials; no additional resources are required (such as dies, cutting tools, coolants, etc.). Despite their wide spread in the most varied areas of production, and their predisposition to environmental sustainability, the issue of AM processes environmental impact has not been adequately analyzed in some essential aspects, such as energy and material consumption, pollution and waste, over the full lifetime of manufactured products (Kellens et al. 2017). Most of the studies in this field have adopted Life Cycle Assessment approaches to analyze the environmental impacts of specific AM processes, converting energy and resources consumption to environmental impact factors (Le Bourhis et al. 2014, Kellens et al. 2014, Faludi et al. 2016). Some authors have summarized the available life cycle inventory data on environmental impacts relative to AM processes, taking into account energy and resources consumption, and emission savings (Huang et al. 2016). Other authors have proposed comprehensive analyses of the studies that have compared environmental impacts related to metal components shaping by either AM and conventional manufacturing techniques (Ingarao 2017). From the existing literature some observations can be made: the results vary widely across these studies, primarily because of the wide variability in data collection methods, material selections, component geometries, which preclude direct comparisons; none of the studies consider environmental sustainability improvements due to changes in material selection or component geometries. As a conclusion, generally the studies in this field are based on a life-cycle impact inventory approach, and do not take into account essential questions, closely related to the main dimensions of the design practice, such as the environmental outcomes due to the relationship that links the choice of material and its required properties to the process parameters, and the key role played by the shape properties of the component to be designed and manufactured. The present paper outlines a Design for Additive Manufacturing (DFAdM) approach that allows to guide the designer towards choices on the shape properties of metal alloy components, such that they are environmentally efficient in their fabrication by additive process. In its formulation, the approach has been developed with reference to the specific class of "powder bed fusion" additive processes for metallic materials (Selective Laser Melting SLM, Electron Beam Melting EBM), in which the volume is built by melting of stratified powder layers, hit by power beams, and for which it has been shown that the energy consumption dominates environmental impact (Faludi et al. 2017). In particular, as a reference process, that of Electron Beam Melting technology has been considered. The quantification of the environmental impact of manufactured components focuses on the estimation of the intrinsic energy consumption of the additive process, that is the energy of the process beam during the various phases of the process, correlating it to the main process parameters, and to some significant features that characterize the shape of the component. Since the use of the intrinsic process energy calculation model requires the definition of the material, on which the setting of the process parameters depends, for the validation phase of the study Ti6Al4V alloy was chosen, a titanium alloy widely used in combination with EBM additive technique. 2. Development of the energy consumption model 2.1. Reference process and material Between powder bed fusion processes, Electron Beam Melting (EBM) has become a metal-based AM technique of consolidated use in a wide variety of fields of application. It uses the energy of an electron beam to melt metal powder layer-by-layer and builds dense parts with limited geometric constraints. Since EBM operates in vacuum conditions, it is particularly appropriate for Ti powder processing, because this element has high affinity for oxygen. Furthermore, when Ti alloys are processed by EBM, the usual problems associated with conventional machining, such as heat generation, friction, use of many tools and consequent long production time, are avoided. Ti6Al4V is the most used Ti alloy thanks to its excellent combination of mechanical properties (strength, fracture toughness, ductility) and corrosion resistance. Ti6Al4V components built by EBM are strictly influenced by process parameters, that are determining for bulk and surface properties, with consequent effects on mechanical behavior